The present invention relates to novel purified and isolated nucleotide sequences encoding mammalian Ca2+/calmodulin stimulated phosphodiesterases (CaM-PDEs) and cyclic-GMP-stimulated phosphodiesterases (cGS-PDEs). Also provided are the corresponding recombinant expression products of said nucleotide sequences, immunological reagents specifically reactive therewith, and procedures for identifying compounds which modulate the enzymatic activity of such expression products.
Cyclic nucleotides are known to mediate a wide variety of cellular responses to biological stimuli. The cyclic nucleotide phosphodiesterases (PDEs) catalyze the hydrolysis of 3xe2x80x2, 5xe2x80x2 cyclic nucleotides, such as cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), to their corresponding 5xe2x80x2-nucleotide monophosphates and are consequently important in the control of cellular concentration of cyclic nucleotides. The PDEs in turn are regulated by transmembrane signals or second messenger ligands such as calcium ion (Ca2+) or cGMP. The PDEs thus have a central role in regulating the flow of information from extracellular hormones, neurotransmitters, or other signals that use the cyclic nucleotides as messengers.
PDEs are a large and complex group of enzymes. They are widely distributed throughout the cells and tissues of most eukaryotic organisms, but are usually present only in trace amounts. At least five different families of PDEs have been described based on characteristics such as substrate specificity, kinetic properties, cellular regulatory control, size, and in some instances, modulation by selective inhibitors. [Beavo, Adv. in Second Mess. and Prot. Phosph. Res. 22:1-38 (1988)]. The five families include:
Within each family there are multiple forms of closely related PDES. See Beavo, xe2x80x9cMultiple Phosphodiesterase Isozymes Background, Nomenclature and Implicationsxe2x80x9d, pp. 3-15; Wang et al., xe2x80x9cCalmodulin-Stimulated Cyclic Nucleotide Phosphodiesterasesxe2x80x9d, pp. 19-59; and Manganiello et al., xe2x80x9cCyclic GMP-Stimulated Cyclic Nucleotide Phosphodiesterasesxe2x80x9d pp. 62-85; all in Cyclic Nucleotide Phosphodiesterases: Structure, Regulation and Drug Action, Beavo, J. and Houslay, M. D., Eds.; John Wiley and Sons, New York (1990).
The Ca2+/calmodulin dependent PDEs (CaM-PDEs) are characterized by their responsiveness to intracellular calcium, which leads to a decreased intracellular concentration of cAMP and/or cGMP. A distinctive feature of cGMP-stimulated phosphodiesterases (cGS-PDEs) is their capacity to be stimulated by cGMP in effecting cAMP hydrolysis.
In vitro studies have shown increased PDE activity in response to Ca2+/calmodulin in nearly every mammalian tissue studied, as well as in Drosophila, Dictyostelium, and trypanosomes. The level of CaM-PDE in tissues and cellular and subcellular compartments varies widely. Most cells contain at least a small amount of CaM-PDE activity, with the highest tissue levels being found in the brain, particularly in the synaptic areas. Greenberg et al. Neuropharmacol., 17:737-745 (1978) and Kincaid et al., PNAS (USA), 84:1118-1122 (1987). A decrease in cAMP in astrocytoma cells in response to muscarinic stimulation may be due to calcium dependent increases in CaM-PDE activity. Tanner et al., Mol. Pharmacol., 29:455-460 (1986). Also, CaM-PDE may be an important regulator of cAMP in thyroid tissue. Erneux et al., Mol. Cell. Endocrinol., 43:123-134(1985).
Early studies suggested that there are distinct tissue-specific isozymes of CaM-PDEs. Several members of the CaM-PDE family have now been described, including a 59 kDa isozyme isolated from bovine heart, and 61 and 63 kDa isozymes isolated from bovine brain. LaPorte et al., Biochemistry, 18:2820-2825 (1979); Hansen et al., Proc. Natl. Acad. Sci. USA, 79:2788-2792 (1982); and Sharma et al., J. Biol. Chem., 261:14160-14166 (1986). Possible counterparts to the bovine 59 and 61 kDa isozymes have also been isolated from rat tissues, Hansen et al., J. Biol. Chem., 261:14636-14645 (1986), suggesting that these two isozymes may be expressed in other mammalian species.
In addition to molecular weight criteria, other evidence supports both similarities and differences among the CaM-PDE family of isozymes. For example, the 59 kDa heart isozyme and the 61 kDa brain isozyme CaM-PDEs differ in mobility on SDS-PAGE and elution position on DEAE chromatography, and the 59 kDa isozyme has at least a 10-20 fold higher affinity for calmodulin. Oncomodulin, a fetal/onco calcium binding protein present in very high concentrations in the placenta and transformed cells, also binds to the 59 kDa enzyme with a higher affinity than to the 61 kDa enzyme. However, both the 61 kDa brain and the 59 kDa heart isozymes are recognized by a single monoclonal antibody. This antibody binds to the Ca2+/CaM-PDE complex with 100-fold higher affinity than to PDE alone. Hansen et al., 1986, supra. The 59 and 61 kDA isozymes have nearly identical substrate specificities and kinetic constants. Krinks et al., Adv. Cyc. Nucleotide Prot. Phosphorylation Res., 16:31-47 (1984) have suggested, based on peptide mapping experiments, that the heart 59 kDa protein could be a proteolytic form of the brain 61 kDa isozyme.
The 63 kDa bovine brain isozyme differs substantially from the 59 and 61 kDa isozymes. The 63 kDa enzyme is not recognized by the monoclonal antibody which binds to the 59 and 61 kDa enzymes. Hansen et al., 1986, supra. The 63 kDa protein is not phosphorylated in vitro by cAMP-dependent protein kinase, whereas the 61 kDa protein is phosphorylated. Further, only the 63 kDa protein is phosphorylated in vitro by CaM-kinase II. Sharma et al., Proc. Natl. Acad. Sci. (USA), 82:2603-2607 (1985); and Hashimoto et al., J. Biol. Chem., 264:10884-10887 (1989). The 61 and 63 kDa CaM-PDE isozymes from bovine brain do appear, however, to have similar CaM-binding affinities. Peptide maps generated by limited proteolysis with Staphylococcal V8 protease, Sharma et al., J. Biol. Chem., 259:9248 (1984), have suggested that the 61 and 63 kDa proteins have different amino acid sequences.
The cGMP-stimulated PDEs (cGS-PDEs) are proposed to have a noncatalytic, cGMP-specific site that may account for the stimulation of cAMP hydrolysis by cGMP. Stoop et al., J. Biol. Chem., 264:13718 (1989). At physiological cyclic nucleotide concentrations, this enzyme responds to elevated cGMP concentrations with an enhanced hydrolysis of cAMP. Thus, cGS-PDE allows for increases in cGMP concentration to moderate or inhibit cAMP-mediated responses. The primary sequence presented recently in LeTrong et al., Biochemistry, 29:10280 (1990), co-authored by the inventors herein, provides the molecular framework for understanding the regulatory properties and domain substructure of this enzyme and for comparing it with other PDE isozymes that respond to different signals. This publication also notes the cloning of a 2.2 kb bovine adrenal cortex cDNA fragment encoding cGS-PDE. See also, Thompson et al., FASEB J., 5(6):A1592 (Abstract No. 7092) reporting on the cloning of a xe2x80x9cType II PDExe2x80x9d from rat pheochromocytoma cells.
With the discovery of the large number of different PDEs and their critical role in intracellular signalling, efforts have focused on finding agents that selectively activate or inhibit specific PDE isozymes. Agents which affect cellular PDE activity, and thus alter cellular cAMP, can potentially be used to control a broad range of diseases and physiological conditions. Some drugs which raise cAMP levels by inhibiting PDEs are in use, but generally act as broad nonspecific inhibitors and have deleterious side effects on cAMP activity in nontargeted tissues and cell types. Accordingly, agents are needed which are specific for selected PDE isozymes. Selective inhibitors of specific PDE isozymes may be useful as cardiotonic agents, anti-depressants, anti-hypertensives, anti-thrombotics, and as other agents. Screening studies for agonists/antagonists have been complicated, however, because of difficulties in identifying the particular PDE isozyme present in a particular assay preparation. Moreover, all PDEs catalyze the same basic reaction; all have overlapping substrate specificities; and all occur only in trace amounts.
Differentiating among PDEs has been attempted by several different means. The classical enzymological approach of isolating and studying each new isozyme is hampered by current limits of purification techniques and by the inability to accurately assess whether complete resolution of an isozyme has been achieved. A second approach has been to identify isozyme-specific assay conditions which might favor the contribution of one isozyme and minimize that of others. Another approach has been the immunological identification and separation into family groups and/or individual isozymes. There are obvious problems with each of these approaches; for the unambiguous identification and study of a particular isozyme, a large number of distinguishing criteria need to be established, which is often time consuming and in some cases technically quite difficult. As a result, most studies have been done with only partially pure PDE preparations that probably contained more than one isozyme. Moreover, many of the PDEs in most tissues are very susceptible to limited proteolysis and easily form active proteolytic products that may have different kinetic, regulatory, and physiological properties from their parent form.
The development of new and specific PDE-modulatory agents would be greatly facilitated by the ability to isolate large quantities of tissue-specific PDEs by recombinant means. Relatively few PDE genes have been cloned to date and of those cloned, most belong to the cAM-specific family of phosphodiesterases (cAMP-PDEs). See Davis, xe2x80x9cMolecular Genetics of the Cyclic Nucleotide Phosphodiesterasesxe2x80x9d, pp. 227-241 in Cyclic Nucleotide Phosphodiesterases: Structure, Regulation, and Drug Action, Beavo, J. and Houslay, M. D., Eds.; John Wiley and Sons, New York; 1990. See also, e.g., Faure et al., PNAS (USA), 85:8076 (1988)xe2x80x94D. discoideum; Sass et al., PNAS (USA), 83:9303 (1986)xe2x80x94S. cerevisiae, PDE class IV, designated PDE2; Nikawa et al., Mol. Cell. Biol., 7:3629 (1987)xe2x80x94S. cerevisiae, designated PDE1; Wilson et al., Mol. Cell. Biol., 8:505 (1988)xe2x80x94S. cerevisiae, designated SRA5; Chen et al., PNAS (USA), 83:9313 (1986)xe2x80x94D. melanogaster, designated dnc+; Ovchinnikow et al., FEBS, 223:169 (1987)xe2x80x94bovine retina, designated GMP PDE; Davis et al., PNAS (USA), 86:3604 (1989)xe2x80x94rat liver, designated rat dnc-1; Colicelli et al., PNAS (USA), 86:3599 (1989)xe2x80x94rat brain, designated DPD; Swinnen et al., PNAS (USA), 86:5325 (1989)xe2x80x94rat testis, rat PDE1, PDE2, PDE3 and PDE4; and Livi et al., Mol. Cell. Biol., 10:2678 (1990)xe2x80x94human monocyte, designated hPDE1. See also, LeTrong et al., supra and Thompson et al., supra.
Complementation screening has been used to detect and isolate mammalian cDNA clones encoding certain types of PDES. Colicelli et al., PNAS (USA), 86:3599 (1989), reported the construction of a rat brain cDNA library in an S. cerevisiae expression vector and the isolation therefrom of genes having the capacity to function in yeast to suppress the phenotypic effects of RAS2va119, a mutant form of the RAS2 gene analogous to an oncogenic mutant of the human HRAS gene. A cDNA so cloned and designated DPD (rat dunce-like phospho-diesterase) has the capacity to complement or xe2x80x9crescuexe2x80x9d the loss of growth control associated with an activated RAS2va119 gene harbored in yeast strain TK161-R2V (A.T.C.C. 74050), as well as the analogous defective growth control phenotype of the yeast mutant 10DAB (A.T.C.C. 74049) which is defective at both yeast PDE gene loci (pdexe2x88x921, pdexe2x88x922). The gene encodes a high-affinity cAMP specific phosphodiesterase, the amino acid sequence of which is highly homologous to the cAMP-specific phosphodiesterase encoded by the dunce locus of Drosophila melanogaster. 
Through the date of filing of parent application Ser. No. 07/688,356, there have been no reports of the cloning and expression of DNA sequences encoding any of the mammalian Ca2+/calmodulin stimulated or cGMP-stimulated PDEs (PDE families I and II) and, accordingly, there continues to exist a need in the art for complete nucleotide sequence information for these PDEs.
The present invention provides novel purified and isolated polynucleotide sequences (e.g. DNA and RNA including sense and antisense strands) which code for expression of mammalian species (e.g., human and bovine) Ca2+/calmodulin stimulated cyclic nucleotide phosphodiesterase and CGMP stimulated cyclic nucleotide phosphodiesterase polypeptides. Genomic and cDNA sequences provided by the invention may be associated with homologous or heterologous species expression control DNA sequences such as promoters, operators, regulators, terminators and the like to allow for in vivo and in vitro transcription to messenger RNA and, in turn, translation of mRNAs to provide functional phosphodiesterases and related polypeptides in large quantities.
Specifically provided by the invention are mammalian DNA sequences encoding phosphodiesterases and fragments thereof which are present as mammalian DNA inserts in bacterial plasmids and viral vectors which are the subject of deposits made with the American Type Culture Collection, Manassas, Va. on Apr. 11 and 15, 1991 and on Apr. 14, 1992 in accordance with U.S. Patent and Trademark Office and Budapest Treaty requirements. DNAs deposited in connection with the present invention include:
1. Plasmid pCAM-40 in E. coli (A.T.C.C. accession No. 68576) containing a bovine brain cDNA insert encoding a 61 kDa CaM-PDE isozyme;
2. Plasmid p12.3A in E. coli (A.T.C.C. 68577) containing a bovine brain cDNA insert encoding a 63 kDa CaM-PDE isozyme;
3. Bacteriophage xcex CaM H6a (A.T.C.C. accession No. 75000) containing a human hippocampus cDNA insert fractionally encoding a 61 kDa CaM-PDE isozyme;
4. Plasmid pHcam61-6N-7 in E. coli (A.T.C.C. accession No. 68963) containing a composite human cDNA insert encoding a 61 kDa CaM-PDE isozyme;
5. Plasmid pcamH3EF in E. coli (A.T.C.C. accession No. 68964) containing a human hippocampus cDNA insert encoding a novel PDE homologous to a 61 kDa CaM-PDE;
6. Plasmid pcamHella in E. coli (A.T.C.C. accession No. 68965) containing a human heart cDNA insert encoding a novel PDE homologous to a 61 kDa CaM-PDE;
7. Plasmid p3CGS-5 in E. coli (A.T.C.C. accession No. 68579) containing a bovine adrenal cDNA insert encoding a cGS-PDE isozyme;
8. Plasmid pBBCGSPDE-5 in E. coli (A.T.C.C. accession No. 68578) containing a bovine brain cDNA insert encoding a cGS-PDE isozyme fragment;
9. Plasmid pBBCGSPDE-7 in E. coli (A.T.C.C. accession No. 68580) containing a bovine brain cDNA encoding a cGS-PDE isozyme;
10. Plasmid pGSPDE6.1 in E. coli (A.T.C.C. accession No. 68583) containing a human heart cDNA encoding a cGS-PDE isozyme fragment;
11. Plasmid pGSPDE7.1 in E. coli (A.T.C.C. accession No. 68585) containing a human hippocampus cDNA insert encoding a cGS-PDE isozyme fragment; and
12. Plasmid pGSPDE9.2 (A.T.C.C. accession No. 68584) containing a human hippocampus cDNA insert encoding a cGS-PDE isozyme fragment.
13. Plasmid pHcgs6n in E. coli (A.T.C.C. accession No. 68962) containing a human cDNA insert encoding a cGS-PDE.
Also specifically provided by the present invention is a bovine cDNA sequence containing nucleotides encoding bovine 59 kDa CaM-PDE and characterized by the DNA and amino acid sequences of SEQ ID NO: 16 and SEQ ID NO: 17.
In related embodiments, the invention concerns DNA constructs which comprise a transcriptional promoter, a DNA sequence which encodes the PDE or a fragment thereof, and a transcriptional terminator, each operably linked for expression of the enzyme or enzyme fragment. The constructs are preferably used to transform or transfect host cells, preferably eukaryotic cells, and more preferably mammalian or yeast cells. For large scale production, the expressed PDE can be isolated from the cells by, for example, immunoaffinity purification.
Incorporation of DNA sequences into procaryotic and eucaryotic host cells by standard transformation and transfection processes, potentially involving suitable DNA and RNA viral vectors and circular DNA plasmid vectors, is also within the contemplation of the invention and is expected to provide useful proteins in quantities heretofore unavailable from natural sources. Systems provided by the invention include transformed E. coli cells, including those referred to above, as well as other transformed eukaryotic cells, including yeast and mammalian cells. Use of mammalian host cells is expected to provide for such post-translational modifications (e.g., truncation, lipidation, and tyrosine, serine or threonine phosphorylation) as may be needed to confer optimal biological activity on recombinant expression products of the invention.
Novel protein products of the invention include expression products of the aforementioned nucleic acid sequences and polypeptides having the primary structural conformation (i.e., amino acid sequence) of CaM-PDE and cGS-PDE proteins, as well as peptide fragments thereof and synthetic peptides assembled to be duplicative of amino acid sequences thereof. Proteins, protein fragments, and synthetic peptides of the invention are projected to have numerous uses including therapeutic, diagnostic, and prognostic uses and will provide the basis for preparation of monoclonal and polyclonal antibodies specifically immunoreactive with the proteins of the invention.
Also provided by the present invention are antibody substances (including polyclonal and monoclonal antibodies, chimeric antibodies, single chain antibodies and the like) characterized by their ability to bind with high immunospecificity to the proteins of the invention and to their fragments and peptides, recognizing unique epitopes which are not common to other proteins. The monoclonal antibodies of the invention can be used for affinity purification of CaM-PDEs and cGS-PDEs, e.g., Hansen et al., Meth. Enzymol., 159:543 (1988).
Also provided by the present invention are novel procedures for the detection and/or quantification of normal, abnormal, or mutated forms of CaM-PDEs and cGS-PDEs, as well as nucleic acids (e.g., DNA and MRNA) associated therewith. Illustratively, antibodies of the invention may be employed in known immunological procedures for quantitative detection of these proteins in fluid and tissue samples, and of DNA sequences of the invention that may be suitably labelled and employed for quantitative detection of mRNA encoding these proteins.
Among the multiple aspects of the present invention, therefore, is the provision of (a) novel CaM-PDE and cGS-PDE encoding polynucleotide sequences, (b) polynucleotide sequences encoding polypeptides having the activity of a mammalian CaM-PDE or of a mammalian cGS-PDE which hybridize to the novel CaM-PDE and cGS-PDE encoding sequences under hybridization conditions of the stringency equal to or greater than the conditions described herein and employed in the initial isolation of cDNAs of the invention, and (c) polynucleotide sequences encoding the same (or allelic variant or analog polypeptides) through use of, at least in part, degenerate codons. Correspondingly provided are viral DNA and RNA vectors or circular plasmid DNA vectors incorporating polynucleotide sequences and procaryotic and eucaryotic host cells transformed or transfected with such polynucleotide sequences and vectors, as well as novel methods for the recombinant production of these proteins through cultured growth of such hosts and isolation of the expressed proteins from the hosts or their culture media.
In yet other embodiments, the invention provides compositions and methods for identifying compounds which can modulate PDE activity. Such methods comprise incubating a compound to be evaluated for PDE modulating activity with eukaryotic cells which express a recombinant PDE polypeptide and determining therefrom the effect of the compound on the phosphodiesterase activity provided by gene expression. The method is effective with either whole cells or cell lysate preparations. In a preferred embodiment, the eukaryotic cell is a yeast cell or mammalian cell which lacks endogenous phosphodiesterase activity. The effect of the compound on phosphodiesterase activity can be determined by means of biochemical assays which monitor the hydrolysis of cAMP and/or cGMP, or by following the effect of the compound on the alteration of a phenotypic trait of the eukaryotic cell associated with the presence or absence of the recombinant PDE polypeptide.